FTP Testing at Higher Elevations

Training
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I have a question about FTP tests at elevation. I’ve recently moved to about 6,800’ from about 500’ and while I was expecting the related decline in FTP, even after acclimatizing (see The Effect of Racing at Altitude | TrainingPeaks which would suggest I should be at ~91% vs. sea level), I feel like something else is going on. When I used to test at the lower elevation, I would sometimes have days where my lungs would give out first and sometimes reached the end due to leg fatigue, but neither ever felt far behind the other. Now when testing at elevation, it’s always my legs that give out first, and always way before I feel like my lungs would give out. Also my HR is much lower when my legs fatigue. My max HR in 2 tests at higher elevation have been 176 and 178, whereas in the last few tests at the lower elevation I maxed out at 190 and 184. It’s a very obvious difference in terms of how my legs start to hurt late in the test, causing me to quit before I feel like I should be ready. What’s happening? Anyone else experience this? Is it something that can be overcome?

One more point of reference, a few outside rides since my most recent test have had very high intensity factors despite me not feeling like I went that hard. For example this morning a 54 minute ride had an IF of .96, and while I was pushing there was definitely more to be had.

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Responding to an old thread here. In a similar position in that home is at 8200’ where I do ramp test and indoor workouts. Many outside rides are at 5300’ so if I do intervals using my 8200’ zones the efforts are way too easy. I have a spreadsheet where I calculate out zones at 0’ and 5300’ based off my 8200’ testing. Lot of extra work, but nobody yet has automated the zone elevation correction to work in real time. I use the updated zones for 5300’ and write the targets on tape on my stem. Old school I know. Your 2nd point on legs vs lungs i get, but I phrase differently. VO2 and above at high elevation are really taxing and take longer to recover for me. I can do them here, but PE is higher and I feel I get better quality work at 5300’. In general I do most VO2 and above work at 5300’ if I can because I can more efficiently recover between intervals. Riding all the time at 8200’ does make 10,000’ casual though.